Devices of this type are used to provide packages, as for example large boxes or loaded pallets, with strappings and in this way hold together the goods stacked on the pallet or the boxes and to secure them for transport. For the production of the strapping, a rigid strap, usually formed from plastics, is laid around the package, the strap ends of which are tensioned against one another with the help of the device and are subsequently connected to one another. With plastic straps, the connection generally takes place with the help of a friction welding unit forming the sealing device.
So as to be able to tension the two strap ends, which are received in the strap channel of the device for the desired tensioning and sealing with the desired tension force against each other, it is necessary to press the tensioning roller during the tensioning process against one of the straps, in general the upper strap end, with a comparatively large force. The tensioning roller is mounted in an overhung position in most of the known devices, so as to enable a simple insertion of the strap ends into the strap channel from its longitudinal outer side and a simple removal of the device from the finished tightening. Due to the floating or overhung mounting of the tensioning roller and the high pressure forces during the tensioning process, the axis or shaft of the tensioning wheel is often deflected thereby causing the tensioning roller to elevate or tilt up at the longitudinal outer side of the strap channel. This in turn causes the pressing pressure exerted by the tensioning roller to the upper strap end, to not be uniform across the width of the strap. Instead, the pressure in the region of the inner strap edge is larger than at the outer edge. The larger pressing force at the inner edge of the tensioned strap end causes a greater (plastic) deformation of the strap (particularly if made of plastic) than in the region of the outer strap edge. That is, the tensioned (upper) strap end becomes thinner in the region of the inner strap edge and at the same time that region becomes longer than at the outer edge, whereby it is deflected in the direction toward the longitudinal outer side of the strap channel and does not lie in an edge exact manner on the other (lower) strap end. The strap ends are then also not connected to one another across their entire width whereby the rigidity of the strap joint or point of strap affixment or tightening suffers.
So as to eliminate this problem, it has been suggested to provide an outer strap edge guide at the longitudinal outer side of the strap channel in the region of the rear face of the strap channel, that is, in the vicinity of the strap sealing device, which guides the upper strap end during the tensioning process at its outer edge and thereby forces it into the strap channel, in which it lies, to the greatest possible extent, in an edge exact edge manner over the lower strap edge. But the additional outer edge guide has a considerable disadvantage in that it significantly hinders the threading of the strap ends into the strap channel and in particular the removal of the device from the finished tightening, as the strap ends or the tightening have to be brought past the outer edge guide. For this, it is generally necessary to provide a complex and a disruption-prone withdrawal mechanism for the outer edge guide, which releases the strap channel for threading the strap ends or removal of the device from the finished tightening at its longitudinal outer side. Alternatively, it has also already been suggested to arrange, against the action of a compression spring, a ball which can be countersunk in a recess in the region of the sealing device as the outer edge guide. This does not need a complicated withdrawal mechanism, but on the other hand, it has not proved to be particularly effective as a guide for the outer strap edge. It is also disadvantageous with the known devices with an additional outer strap edge guide that straps with different widths can only be processed with one device if the width of the strap channel between the inner and the outer strap edge guide is changed with an often considerable effort.